Merge branch 'ab/hook-tests-updates'

Update tests around the use of hook scripts.

* ab/hook-tests-updates:
  http tests: use "test_hook" for "smart" and "dumb" http tests
  proc-receive hook tests: use "test_hook" instead of "write_script"
  tests: extend "test_hook" for "rm" and "chmod -x", convert "$HOOK"
  tests: use "test_hook" for misc "mkdir -p" and "chmod" cases
  tests: change "mkdir -p && write_script" to use "test_hook"
  tests: change "cat && chmod +x" to use "test_hook"
  gc + p4 tests: use "test_hook", remove sub-shells
  fetch+push tests: use "test_hook" and "test_when_finished" pattern
  bugreport tests: tighten up "git bugreport -s hooks" test
  tests: assume the hooks are disabled by default
  http tests: don't rely on "hook/post-update.sample"
  hook tests: turn exit code assertions into a loop
  test-lib-functions: add and use a "test_hook" wrapper